A little over three years ago, I built Rhythm Brother the following machine:
Video Card: EVGA 7800 GTX (PCI-Express)
Motherboard: Epox 9NPA+ Ultra
CPU: AMD Athlon 64 3700+ (939 pin)
2 GB RAM
Win XP
Various doodads and drives that probably aren’t relative to this thread
On a couple occasions he’s asked me if it’s time to upgrade his card. Because I have the same graphics card but an SLI-compatible motherboard, I don’t think I can be quite trusted on this one 
I’m also not sure if he’s really asking, or if I’m missing some hint and should just go about enabling the upgrade.
For playing HL2, Bioshock, and other games his system can handle, would upgrading to an eight or nine series video card make a noticeable difference?
Oh, I’m assuming he’d give me his old card (hence the self interest). I know we’re wayyyy past the EVGA trade-up period. Other than E-bay, are there resellers who would take a trade-in?
Thanks,
Rhythm
Well, I just purchased the GeForce 8800 GT 512MB 256-bit GDDR3 and for the price I must say I’m blown away. It’s even been mentioned that this card kind of cannibalizes some of Nvidia’s higher end cards because of the quality. It’s definitely worth looking into.
Check out Newegg
edit: Oh and it’s also SLI capable, so if it isn’t enough for him, he can just plug in another one
Best bang for the buck at the moment is the 9600GT, but the new GTX 260 and 280 are due out imminently which should push prices down even further. But really, is he getting slow framerates? If he’s getting decent performance in the games he plays then don’t bother upgrading.
Of course, what you could do is upgrade your own PC and give him your old video card and motherboard to SLI… 
Well, if you don’t upgrade now, when will you upgrade? If you have the money, go for it. A brand new video card will insure that he can play the next generation of games, and his older games will run lightning fast at the highest detail levels.
Since he is asking, he must be noticing the limitations of his current card. This comparison is a little old, but shows HL2 frame rates in different situations with different cards. The oldest Geforce is the 7900GTX, which seems to perform just a bit better then the 7800GTX.
Since there is something in this for both of you, I’m sure you can work out a deal. 
That’s the thing—I don’t think he’s having any problems or concerns with HL and whatnot, just that he’s wondering if upgrading will noticeably improve things. That’s a great chart/review CoG888 (love Anandtech… glad to see the porn squatter doesn’t seem to be there anymore), and sure makes things look like there’ll be a huge improvement.
But if he’s already got all video settings turned up to the max and he’s not having any noticeable issues, will upping the card do anything more than make his inner latest-tech monkey happy? That is, will the shaders and polygon engines be able to draw even more information on the screen, changing the visuals? Will it allow him to play more modern games, adding life to a three-year old system?
Also, in the interim he went from a CRT to an LCD screen. Again, I don’t believe he’s having problems/artifacts, but could a newer card drive the screen visually differently?
No, a new card is not going to make his games better if he can already run with the highest resolution/detail settings. The only advantage to upgrading is, as you said, “adding life to a three-year old system.” Except for a RAM upgrade at some point, a new video card is the only upgrade that system will need in the next few years to keep up with newer games. If the cost of a new card is not an issue, I’d say buy it. If you would rather get the best value out of your purchase, wait until his newest games demand a better card.
Wait until he has a game that needs a better video card. He might just possibly benefit if you upgraded him to 4 GB and 64 bit Vista, assuming all his apps work in Vista, that is. The increase in memory will improve his minimum frame rate.